While the methods, compositions, and materials presented herein can be used in a variety of applications, they are well adapted for use with respect to orthopedic support materials, such as casting tapes. Therefore, as background, characterizations of technology relating to orthopedic casting tapes and problems overcome by the present invention are provided.
Orthopedic casting tapes have been produced using curable resins coated or impregnated onto a substrate. Typically, the casting tape is stored as a roll in a water-impermeable storage pouch until needed for use. When needed, the roll of tape is removed from the pouch and contacted with water. Generally, the tape includes a resin therein that is water-curable. Thus, shortly after the tape is dipped in water, the resin will begin to cure and the tape harden. A medical practitioner applies the casting tape to a patient immediately after it has been immersed in water. Generally, resin materials are chosen that begin to cure immediately after being dipped in water, and that will harden sufficiently to resist passive motion in a joint, i.e., a wrist or ankle, in 3-5 minutes, and to be weight bearing within about 30 minutes.
Typical resin coatings utilized in conventional orthopedic casting systems include isocyanate-functional polyurethane prepolymers. Generally the resin coatings also include lubricants to facilitate unrolling, application, and molding without the resin interfering. Furthermore, they often include defoaming agents to maintain porosity while carbon dioxide is evolved during the curing process. When exposed to water, the isocyanate functional polyurethane prepolymers cure to form polyureas. In certain situations, it may be desirable to avoid or reduce the level of such reactive groups and products.
Typical substrates upon which the above resin coatings are applied to produce an orthopedic casting tape are knit fabrics prepared from glass and/or synthetic fibers. Fiberglass or other high modulus fibers contribute significant strength to the cured resin/substrate composite as well as provide a reservoir for the resin during storage and end-use application of the casting tape. Nonglass and low modulus substrates generally provide for a lower weight and more radiolucent cast. Here the strength is limited by the amount of resin that can be held by the substrate. High resin loading with materials known to date must generally be avoided, however, to prevent excessive heat build-up in the cast while it is in its early stages of cure, i.e., during hardening, as a result of the exotherm produced in the above resins. Furthermore, high resin loads with conventional resins must generally be avoided to prevent undesirable pooling of the resin. "Pooling" is the uneven distribution of the resin on the substrate as a result of the flow of resin due to gravity.
Orthopedic casting tapes of this type are described in U.S. Pat. Nos. 4,667,661 and 4,774,937 (Scholz et al.), which are owned by Minnesota Mining and Manufacturing Company of St. Paul, Minn., the assignee of the present invention. Such tapes are also commercially available from 3M Company under the tradenames Scotchcast.RTM. Plus casting tape and Scotchcast.RTM. 3 casting tape. Construction materials of this type are also described in U.S. Pat. Nos. 4,411,262 and 4,570,622 (von Bonin et al.). These materials are one-component systems containing isocyanate or alkoxysilane groups, i.e., silyl-substituted urea, biuret, and urethane derivatives.
A need exists for a water-curable resin composition that can be used in a wide variety of orthopedic support materials, whether used in combination with a fiberglass substrate or a nonglass low modulus substrate. That is, a need exists for a resin composition that can be used in large amounts, i.e., at high resin loads, without excessive heat build-up, resin pooling, and/or perceived health hazards, as well as in smaller amounts.